Your brain's reset key is Zzzz

As a teenager, like many of you I’m sure, I neglected sleep. It seemed that partying all night and then working hard at school all day was the obvious solution to an overbooked schedule. I was rudely awakened a few years later when a good night’s sleep became necessary to merely function the next day (also when I realized what it really meant to have an overbooked schedule). While we know that sleep is essential for survival (at some point, coffee just doesn’t cut it), we know very little about why sleep is so important, and what happens to our brain while we sleep. In a recent issue of Science, a team of researchers made a contribution to this field using sleep-deprived fruit flies.

In the study, researchers looked at synapses, the junctions between brain cells (called neurons). Synapses are important because they relay information from one neuron to the next. Through synaptic connections, neurons form networks, and these networks underlie many complex brain functions like perception and thought.

The researchers cleverly engineered fruit flies to make their synaptic connections fluorescent (for those of you who read my first post, this is an excellent use of GFP). Subsequently, the researchers took images of the flies’ brains, and were able to count the brightly fluorescent synapses. The study first established that flies that hang out with other flies (this is called social enrichment) have more synapses than lonely flies. While this finding is interesting on its own, the researchers didn’t stop there. They took the socially enriched flies and divided them in two groups. The first group of flies was allowed to sleep as much as they wanted for 48 hours while the second group of flies was sleep deprived for 48 hours. Which group of flies do you think had more synapses after the experiment?

Well, the study shows that flies that slept had much fewer synapses than the sleep-deprived ones. Does it surprise you?

Initially, I thought this was a little counter-intuitive. With all this talk about sleep being important for performance and memory, I would have thought that the flies that slept would have had more connections between brain cells. This study suggests exactly the opposite, and shows that sleep acts to downscale the synapses that are created while the flies are awake and experiencing new things. When you think about it, this finding makes sense. If there was no way to “reset” those synapses, we can hypothesize that every time you learn or experience something new, you would get more and more connections between your brain cells. Eventually, we can imagine it would be a complete mess up there, and connections might saturate, leaving no room for anything new. Downscaling your synapses at night while you sleep also helps eliminate the unimportant connections, thereby making the stronger synapses stand out.

So what’s the take-home message? Enough procrastinating on the internet, go to bed!

Reference: Use-dependent plasticity in clock neurons regulates sleep need in Drosophila. Donlea JM, Ramanan N, Shaw PJ. Science. 2009 Apr 3;324(5923):105-8.